The present invention relates to exhaust systems for vehicles having internal-combustion engines. More particularly, the present invention relates to an exhaust system for a vehicle that includes an improved silencing system for an exhaust manifold of the vehicle which complements the silencing capability of the muffler system to improve the overall performance of the total exhaust system.
Conventional exhaust systems for vehicles having internal-combustion engines generally include an exhaust manifold for gathering exhaust pulses from one or more cylinders. The exhaust manifold is then coupled through an exhaust pipe to a muffler that is intended to dampen the sound produced by the engine. In most vehicles, the muffler is spaced-apart from the engine and exhaust manifold by a considerable distance. Generally, the pipe connecting the exhaust manifold and the input of the muffler is necessarily formed to include several turns and bends so that it can be routed through the vehicle structure to the location where the muffler is mounted on the vehicle.
Noise in the exhaust system arises from acoustic pressure waves that are generated by the sudden release of exhaust gases from the individual cylinders of the vehicle engine. These acoustic pressure waves travel from the exhaust manifold through the exhaust pipe to the muffler. In most vehicles, the exhaust manifold collects exhaust pulses from more than one cylinder. Because these exhaust pulses are emitted into the exhaust manifold at different times, the pulses create acoustic pressure waves that may interact with each other to cause acoustic pressure points within the exhaust system where the acoustic pressure is increased. Further, as the pressure waves travel through the exhaust pipe toward the muffler, each bend and turn in the pipe changes the pressure waves somewhat. Generally, the pressure waves are changed because each bend or turn in the pipe reflects a portion of the wave, which causes the reflected waves to interfere with the primary waves to change the frequency of the acoustic pressure waves as they travel toward the muffler. Thus, although the pressure waves emitted into the exhaust manifold from the engine are of a generally uniform frequency, as the pressure waves interact and travel through the exhaust pipe toward the muffler, the frequency spectrum of the acoustic waves is generally increased somewhat.
In order to dampen these acoustic waves to reduce the sound emitted by the vehicle, it is known to incorporate resonance chambers in the muffler which act to attenuate the acoustic waves. A known type of resonance chamber is a Helmholtz resonator which generally consists of a cavity chamber that includes an input tube which communicates with the flow of the acoustic pulses or waves in the muffler. As the acoustic waves travel along the interior of the muffler, the pulsating waves impact upon the input tube to the cavity chamber which creates pressure variations within the chamber. These pressure variations within the chamber tend to attenuate or dampen the amplitude of the acoustic waves. Thus, the resonance chamber absorbs energy from the acoustic waves, which acts to silence somewhat the noise emitted from the muffler. In addition, acoustic energy that enters the cavity is returned to the muffler with a phase relationship that causes the returned energy to be reflected back toward the source. The resonance chamber is frequency specific, in that a specific resonance chamber is only able to dampen and reflect acoustic waves of a very narrow frequency band or spectrum. If the resonator is located in a position at which the acoustic waves in the system are varying with a particular frequency the resonator is tuned to suppress, the resonator will absorb energy from the acoustic wave. Because the frequency spectrum of the acoustic waves generally increases considerably as they travel toward the muffler, it is generally necessary to include several resonance chambers of different sizes in the muffler to dampen the acoustic waves of different frequencies.
One problem with the known type of exhaust systems is that the muffler must include several different sizes of resonance chambers in order to adequately attenuate the different frequencies of the acoustic waves as they reach the muffler. This normally increases the size and complexity of the muffler considerably.
Another problem with the known exhaust systems is that, depending upon the engine type, it is sometimes extremely difficult to attenuate the acoustic waves to an acceptable level simply by using resonance chambers in the muffler. It is known to add a separate resonator component near the muffler in the exhaust system to increase the attenuation of the acoustic waves in some systems. However, this increases the complexity of the system by requiring another component, and also increases the cost of the exhaust system.
One object of the present invention is to provide an exhaust system that exhibits increased attenuation of exhaust noise over the known systems.
Another object of the present invention is to provide an exhaust system that exhibits increased attenuation without the necessity of increasing the complexity and size of the muffler component itself.
Yet another object of the present invention is to provide an exhaust system in which a resonance chamber is provided in the system at a location where the frequency spectrum of the acoustic waves produced by the engine is relatively narrow.
According to the present invention, an exhaust manifold for attachment to an engine having a plurality of exhaust ports is provided. The exhaust manifold includes an exhaust conduit that is in fluid communication with selected exhaust ports, with the exhaust conduit being formed to include separate primary and auxiliary outlet openings. The exhaust manifold also includes a tuning tube that is formed to include an inlet opening that is in acoustic communication with the auxiliary outlet opening, and an outlet opening. The exhaust manifold also has chamber means for providing a static volume that is in acoustic communication with the outlet opening of the tuning tube.
One feature of the foregoing structure is that a tuning tube and corresponding chamber means are provided in the exhaust manifold for attenuating a selected frequency spectrum of the acoustic or sound pressure waves generated by the engine. One advantage of this feature is that by locating the tuning tube and chamber means in the exhaust manifold, the tuning tube and chamber means are located at the optimum position within the exhaust system of the vehicle to attenuate the sound pressure waves emitted by the engine most efficiently. Another advantage of the foregoing structure is that by locating the tuning tube and chamber means in the exhaust manifold, a single tuning tube and chamber means are able to attenuate a significant portion of the sound emitted by the engine, without the necessity of providing a plurality of tuning tubes and chamber means.
In preferred embodiments of the present invention, the tuning tube has a predetermined diameter and effective lengt that are selected to cause the tuning tube and the chamber means to cooperate to attenuate at least a predetermined frequency present in the exhaust conduit during discharge of combustion product through the exhaust ports upon operation of the engine. One feature of the foregoing structure is that the dimensions of the tuning tube are selected to cooperate with the chamber means to attenuate a predetermined frequency spectrum created by the exhaust pulses of the engine before the frequency spectrum of the exhaust pulses or acoustic waves has increased. One advantage of this feature is that the tuning tube can be selected to attenuate the primary noise producing acoustic waves before these acoustic waves have exited the exhaust manifold. This permits the tuning tube to be closely matched with the frequency of the maximum noise producing acoustic waves.
Also in preferred embodiments of the present invention, the predetermined location of the auxiliary outlet opening is selected to position the auxiliary outlet opening in close proximity to an acoustical pressure point in the exhaust conduit. One feature of the foregoing structure is that the inlet to the tuning tube is positioned in close proximity to the location of one of the acoustical pressure points in the exhaust conduit. One advantage of this feature is that by locating the tuning tube in such a position, the frequency attenuation characteristics of the tuning tube and the chamber means are enhanced.
Also in preferred embodiments of the present invention, the chamber means is configured to surround the exhaust conduit to provide a static volume for the tuning tube and in addition, to provide insulation means for retaining heat energy in the exhaust conduit. One feature of the foregoing structure is that the chamber means functions to provide both the static volume for the tuning tube, and insulation means for the exhaust conduit. One advantage of this feature is that the chamber means acts to limit heat energy dissipation to the surrounding engine compartment so that heat energy in the combustion product is discharged substantially through the primary outlet opening.
Thus, the exhaust manifold of the present invention provides improved silencing for the entire exhaust system by attenuating selected noise frequencies emitted by the engine directly in the exhaust manifold. By controlling selected noise frequencies directly in the exhaust manifold, these selected frequencies can be substantially attenuated before they exit the exhaust manifold. This increases the silencing ability of the entire exhaust system because the muffler in the system will have fewer acoustic frequencies to attenuate. Thus, the silencing capability of the entire exhaust system is enhanced without increasing the size or complexity of the muffler itself.
Additional objects, features, and advantages of the invention will be apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.